The present invention relates to a vacuum distillation plant and a process for concentrating organic aqueous solvent mixtures, especially spissum extracts, using said plant.
One route for preparing drugs on plant basis is extracting the plant material and processing the extracts and tinctures obtained into dry extracts. As a rule, aqueous, alcoholic or mixed aqueous/alcoholic extracts are prepared, ethanol generally being used as the alcoholic component. However, the extracts may contain additional organic solvents such as methanol, propanol, butanols as well as ethers and ketones (especially ethyl ether and acetone). The extracts or tinctures thus obtained are used as such or concentrated to so-called spissum extracts which may then be processed into dry extracts. Concentration of organic aqueous solvent mixtures is generally conducted by bubble or surface evaporation. As a result of contact with hot surfaces, undesirable conversions may occur which may lead to a decrease of the content of active ingredients. Since the more volatile component of the solvent mixture is evaporated first using a distillation method of the prior art, the water level increases. This water level is primarily responsible for germ growth. The pertinent pharmacopoeias define the bacterial counts for bacteria, yeasts and molds.
When selecting a non-sterile starting product, which is unavoidable in the production of plant extracts, the bacterial count in the finished end product is directly related to the processing time.
DE 195 25 026.5 provides a process for drying spissum by using a multi-blade stirrer which reduces the drying time considerably without being harmful, but this process encounters problems of capacity. In order to avoid having to use this process for spissum preparation, concentration under similarly inoffensive conditions that would not harm the product would be necessary. Such an industrial or commercial scale process is not known.
Thickening or vaporizing is generally conducted by conventional distillation. However, conventional distillation has various disadvantages when used to thicken or vaporize spissum extracts or general aqueous alcoholic solutions. For a start, a considerable amount of energy is required to vaporize highly polar solutions such as water or alcohol. For example, about 1 KW of energy is needed to evaporate 1 kg of water in conventional evaporator systems, which is 15 times the amount required to distill polar solvents such as toluene. As far as the apparatus is concerned, large surface areas in the heat exchangers and continuous introduction of heat are required. Consequently, processes without heat recovery are highly unprofitable.
Since the more volatile solvent is first distilled off from solvent mixtures, operators are also facing the problem that the ratio of the solvents in the bottoms product changes continuously. However, in case of plant extracts, reduction of the alcohol content, which constitutes the more volatile component in aqueous alcoholic solvent mixtures, results in undesirable precipitation of extracted materials. In extreme cases, this means that first the alcohol and then, in a second run, the water is distilled off in a batch process in order to achieve concentration of the bottoms product. However, this results in segregation of the product.
As mentioned above, conventional distillation processes also requires the continuous addition of heat. This conflicts with the high temperature sensitivity of most active ingredients derived from plants which are usually protected by applying a vacuum during distillation. Even though this permits a decrease of the operating temperature of the distillation process, heat still needs to be introduced which results in a considerable strain on the interfaces in the bottoms product to be concentrated.
Finally, vaporising of aqueous alcoholic plant extracts also creates the problem of foam formation in some plants. In order to avoid the formation of foam, the surface tension of the bottoms product must be reduced by adding alcohol. Distilling off the alcohol increases the problem of foam formation. In extreme cases, such foam formation causes flooding of the distillation apparatus so that the process needs to be interrupted and production stopped.
In order to solve the problem of high energy consumption, attempts have been made to use different distillation processes including heat recovery employed in other technical fields. Among those processes, an open heat pump with mechanical concentration appears to be the most economical. For example, 50 Watts/kg are required for distilling water which corresponds to an energy consumption 20 times lower than in conventional distillation. Specifically, the distillation plant based on the principle of an open heat pump, which is known from the prior art, operates with mechanical concentration of the vaporized product (concentration of the overhead product). The overhead released under vacuum in the evaporator is volumetrically withdrawn from the concentration means, concentrated with additional heating and then precipitated in a condenser. The energy of condensation is channeled directly to the evaporation process. This results in an energy saving process which is kept going by the concentration means alone without heating or cooling, permitting a considerable reduction of the amount of heat required.
Depending on the solution to be distilled, the plant may be operated with a bubble evaporator or a flash evaporator. When a bubble evaporator is used, the heat exchanger is located in the bottoms space of the medium to be distilled, while, in a flash evaporator, a circulating pump transports the bottoms product through the heat exchanger and recycles it to the evaporator in a heated state, where it is expanded for distillation. Such plants are used to concentrate baths and rinses from degreasing, phosphatisation, chromatisation and galvanization, for cooling lubricant emulsions, vibratory grinding emulsions, compressor condensates or washing solutions from washing cabins and high-pressure cleaning devices. The distillate (waste water) may be fed into the regular sewer, while a highly concentrated concentrate, which needs to be disposed of, is recovered as the bottoms product. In the case of solvent mixtures, however, this type of distillation process is still encumbered by the problem that the more volatile solvent is distilled off first with the result that the ratio of the solvents in the bottoms product shifts. Therefore, plants of the prior art are not suitable either for concentrating aqueous alcoholic solutions such as plant extracts.